default.hpp

#pragma once

#include <sps/optional>

namespace sps {

struct DefaultValue {};
static const DefaultValue defaultValue;

template<typename T>
using IsNotReference =
  typename std::enable_if<!std::is_reference<T>::value, void>::type;

template<typename T, T... DefaultedParameter>
class Defaulted {
 public:
  // Do not make these explicit
  Defaulted(T const& t) : value_(t) {}

  template<typename T_ = T, typename = IsNotReference<T_>>
  Defaulted(T&& t) : value_(std::move(t)) {}

  Defaulted(DefaultValue) : value_(DefaultedParameter...) {}
  T const& get_or_default() const {
    return value_;
  }
  T & get_or_default() {
    return value_;
  }
 private:
  T value_;
};

template<typename T, typename GetDefaultValue>
class DefaultedF {
 public:

  DefaultedF(T const& t) : value_(t) {}

  template<typename T_ = T, typename = IsNotReference<T_>>
  DefaultedF(T&& t) : value_(std::move(t)) {}

  DefaultedF(DefaultValue) : value_(sps::nullopt) {}

  template<typename... Args>
  T get_or_default(Args&&... args) {
    if (value_) {
      return *value_;
    } else {
      return GetDefaultValue::get(std::forward<Args>(args)...);
    }
  }
 private:
  sps::optional<T> value_;
};
}  // namespace sps

/* Local variables: */
/* indent-tabs-mode: nil */
/* tab-width: 2 */
/* c-basic-offset: 2 */
/* End: */